History for ZRender

??changed:
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ZRender objects implement the ZRenderer Proposal

o A ZRender object has attributes corresponding to the atttributes of the
  original tag.

o When called, it attempts to acquire the method named by the 'z-render'
  attribute.  If this fails, either an exception is raised or the original
  tag is inserted.

o The object pushes itself onto the namespace stack and calls the acquired 
  method.

o The return value of this method is passed through to the ZRender
  object's caller.

o The ZRender object exposes methods to manipulate its attributes, and
  has a __str__ method which represents the object as a tag with the
  current attributes.